在书面语中，条件从句可以不用连词if，而将谓语中的过去式were，had或 should 等移至主语之前。如：

Were you in my position, what would you do?

假如你处在我的位置，你会怎么做？

Were he to leave today, he would get there by Friday.

如果他今天动身，星期五前会赶到那儿。

Had some work been done, energy would have been applied.

如果做了一定量的功，就一定消耗了能量。

Had they time, they would come to see you.

如果他们有时间，他们就会来看你。

Should it rained tomorrow, the meeting would be postponed.

万一明天下雨，会议就会延期。

Should he come, he would be able to examine the trial run of the machine.

如果他来，他就能检验这台机器的试车情况了。

情态助动词用于虚拟语气

有不少情态助动词也可用于虚拟语气。如：

May you live a long and happy life.

愿你长寿幸福。（may只用于表示愿望）

If there were no friction, an automobile could not move.

没有摩擦力，汽车就不能开动。

But for your help, we couldn’t have succeeded.

要不是你的帮助，我们是不会成功的。

If computers had not been invited, many problems on space flight could not have been solved.

如果没有发明计算机的话，宇宙飞行的许多问题就不可能解决。